Add countryIso to time zone result

For countries that share the same MCC, a NITZ is required to narrow down the country ISO. Once we have found the country, we return it to the LocaleTracker via OffsetResult, along with the time zone.

Test: atest FrameworksTelephonyTests
Bug: 393349646
Flag: com.android.internal.telephony.flags.allow_multi_country_mcc

Change-Id: Ie970562b871126278995e1c115c47e6dc48956dd